The present invention relates to a process for the thermocatalytic conversion of waste organic materials, including used tire rubber, waste plastics, and used motor oils and lubricants, into lower molecular weight hydrocarbons and the concomitant recovery of solids present in the initial feedstocks.
Currently in every industrialized country in the world there are huge quantities of discarded used tires that are a haven for vermin and insects, as well as being a serious fire hazard. For example, in the United States by recent estimates, approximately 260 million tires are discarded each year. In addition to the flow of newly generated scrap tires, it is estimated in excess of 2 billion scrap tires are already stored in piles around the United States. The situation is essentially the same around the world. There has been considerable research and development into providing a solution for the disposal of used tires.
A substantial effort has been directed toward finding uses for used tires. Of these estimated 260 million used tires discarded each year, as much as 70% have potential uses as fuel in various kilns and boilers while about 13% are used in rubber product applications, both supported by partial subsidies. There is a modest consumption of used tires comminuted to crumb rubber for use in molding and sheeting of low value rubber products. The majority of disposal techniques studied, such as pyrolysis, are for technical reasons generally unable to support themselves economically.
Tires generally are composed of rubber, carbon black, steel, fabric, and additives. Styrene-butadiene rubber is most commonly used in tire manufacture, usually in combination with other elastomers such as natural rubbers, isoprenes, and ethylene-propylene diene rubbers. Various carbon blacks, sometimes blended with finely divided silica, are used in tires to strengthen the rubber and improve the resistance of the rubber to abrasion. It is not unusual that as many as four or five different carbon blacks are used in building a single tire. Other additives, such as extender oils, antioxidants, and antiozonates are used in tire manufacturing to slow the atmospheric oxidative cracking of the tire rubber. Finally, a small percentage of fillers, such as titanium dioxide, a pigment, may be present to provide such things as the esthetics of white wall tires.
The synthesis of tire rubber is a polymerization process. Polymerization is a process wherein individual monomers, such as styrene and butadiene, join together in large numbers to form a polymer molecule. When two dissimilar molecules, such as styrene and butadiene, join together to form a polymer chain, a copolymer is produced. There are two broad classes of polymers and copolymers based on their polymerization procedure. One class is based on condensation polymerization, producing condensation polymers, such as polyesters, nylons, polycarbonates, and polyurethanes. These polymers have a molecular weight lower than the sum of the molecular weights of the monomers used to produce them. The other class of polymers are known as addition polymers, whose molecular weight is the sum of the molecular weights of the monomers used to make them. Addition, or chain growth polymers, are made in specific conditions of temperature and pressure and in the presence of a catalyst or reaction initiator. SBR (styrene butadiene rubber), EPDM (ethylene propylene diene monomer) rubber, polyethylene, polypropylene, and polystyrene, to name a few, are addition polymers.
In addition to used tires, a considerable tonnage of waste commodity plastics, or polymers, are improperly disposed of each year. In the last few years, there has been considerable improvement in the collection and recycling of common waste polymers. However, the recycling and reuse of waste polymers, as now practiced without subsidies, has proven to be uneconomic, forcing the abandonment of many recycling efforts. The recycling of waste polymers as fuel has not proven practical because of the inability to collect sufficient quantities to sustain operation.
Finally, in addition to used tire rubber and waste commodity plastics, a significant quantity of used motor oil, lubricants, and various other organic chemicals are disposed of wastefully. This quantity of disposed motor oil and lubricants represents a significant waste of a potential source of base organic chemicals that, if recovered, could be used in a variety of applications. Thus, a better way of converting waste organic chemicals is needed.
There have basically been two methods to break down used tire rubber, waste polymers, used motor oil and lubricants, and other waste organic materials into base organic chemicals that can be reused: pyrolysis and depolymerization. Of these two methods, the most commonly employed has been pyrolysis, in which the waste organic material feedstock is converted into commercial products such as hydrocarbons and carbon blacks. Pyrolysis is the thermal degradation in the absence of oxygen. It is commonly conducted at temperatures in the range of 650xc2x0 to 800xc2x0 C. Pyrolysis, because of the conditions at which it is employed, commonly results in the production of low value hydrocarbons and low quality, low activity carbon black. Despite assertions to the contrary, no pyrolysis process is known to have been in operation for sustained periods producing valuable reinforcing grade carbon blacks at a profit. Thus, current, and probably any future, pyrolysis processes are liable to be both technically and economically unattractive.
In depolymerization processes, a given polymer, subjected to conditions above its depolymerization temperature, breaks down into the individual monomers that comprise the polymer. For example, polystyrene and polypropylene will depolymerize into styrene and propylene, respectively. Accordingly, depolymerization processes are not capable of producing a wide range of hydrocarbons that can be used to produce compounds other than the same polymers initially subjected to the depolymerization process.
In view of the foregoing, a desirable process would be capable of processing waste organic materials, including waste tire rubber as well as waste plastics, regardless of its source or composition, to yield hydrocarbons. These hydrocarbons could be used to produce the base organic compounds of the initial waste organic materials subjected to the process but could additionally be used to produce entirely different compounds. A desirable process would also be capable of processing other waste organic materials, such as used motor oil and lubricants. A desirable process would also be capable of separating and/or recovering solids present in these initial feedstocks. Moreover, the presence of antioxidants and antiozonates would not pose a problem for such a desirable process. Additionally, a desirable process would be able to accommodate at least some level, albeit of reduced size, of steel fibers, fiberglass, and/or fabric that might be present in the initial feedstock of waste organic materials, particularly a feedstock comprising used tire rubber. A desirable disposal process should be able to simultaneously process several commingled dissimilar feedstocks, such as tire rubber, used motor oil, waste polymers, waste lubricants, and others. The present invention directed to a thermocatalytic conversion process provides the aforementioned needs.
In accordance with one aspect of the invention, there is provided a continuous process for the thermocatalytic conversion of a feedstock of waste organic materials into reusable hydrocarbons. The process entails providing the feedstock and a catalyst comprising aluminum trichloride (AlCl3) to a heated, stirred reactor maintained at pressures and at temperatures sufficient to maintain AlCl3 as a fluid. The process can be conducted in 3 modes: (1) low reactor pressure, (2) partial vacuum, and (3) high reactor pressure.
As feedstock is converted into vaporized hydrocarbons, vaporized hydrocarbons and vaporized AlCl3 are removed from the reactor. AlCl3 and a certain fraction of the hydrocarbons can be subsequently condensed and returned to the reactor. The composition of the condensed hydrocarbon fraction is controlled based on vapor pressure. The remaining uncondensed vaporized hydrocarbon is recovered as product.
In accordance with another aspect of the invention, a reactor discharge portion is also removed from the reactor. This portion may contain unreacted feedstock and AlCl3 catalyst. The reactor discharge portion is provided to a supplemental reactor maintained at temperatures sufficient to generate additional vaporized hydrocarbons and to vaporize residual AlCl3. The additional vaporized hydrocarbons and additional vaporized AlCl3 catalyst are removed from the supplemental reactor and provided to a recycle catalyst condenser wherein the hydrocarbons are separated for recovery and wherein at least a portion of the additional vaporized AlCl3 is condensed and returned to the reactor. Make-up catalyst is provided to the recycle catalyst condenser and then to the reactor to maintain appropriate catalyst to feedstock ratios. While the entire quantity of additional hydrocarbons provided to the recycle catalyst condenser can be recovered for subsequent uses, a fraction may be condensed and returned to the reactor.
In accordance with another aspect of the invention, any remaining residuals contained in the supplemental reactor are subjected to subsequent processes to recover carbon black.